fix: refresh stale browse cache on track edits and allow deleting empty releases

- Add CmsTrackBrowserViewModel.Invalidate(); called from TrackEdit/BatchEdit on save or delete so album/genre cache is invalidated and re-fetches on next mode switch
- CmsAlbumBrowser now handles 0-track releases: confirm dialog + DeleteReleaseAsync instead of early return; partial-failure path also fires OnReleasesChanged to trigger cache invalidation
- TrackList.OnAlbumsChanged now calls VM.Invalidate() so genres stay fresh after any album delete
- UnifiedTrackService.DeleteAsync cascades release soft-delete when last live track is removed (non-fatal; logs on failure)
- New DELETE api/track/release/{id} endpoint (ApiKeyAuthorize) for direct release soft-delete
- EF migration SoftDeleteOrphanedReleases backfills existing orphaned release rows via raw SQL (data-only, no schema change)

DeepDrftData/ITrackService.cs

@@ -39,4 +39,13 @@ public interface ITrackService
     Task<ResultContainer<TrackDto>> Create(TrackDto newTrack);
     Task<ResultContainer<TrackDto>> Update(TrackDto track);
     Task<Result> Delete(long id);
+
+    /// <summary>Soft-delete a release row by id. Idempotent — a missing or already-deleted row is a no-op.</summary>
+    Task<Result> DeleteRelease(long id, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Count of non-deleted tracks on a release. Backs the delete-cascade decision: when a track
+    /// delete leaves a release with zero live tracks, the release is soft-deleted too.
+    /// </summary>
+    Task<ResultContainer<int>> CountLiveTracksByRelease(long releaseId, CancellationToken cancellationToken = default);
 }